The present invention relates to a method and system for controlling the operation of a two-stroke engine and an arrangement which permits the purging of a determinable amount of fluid from a cylinder of such an engine such that a proper air/fuel ratio exists.
Advantages of a two cycle engine are reduced cost and simplicity of construction. These engines, however, do have significant drawbacks. There is always some residual, sometimes significant, amount of burnt gases that remain in the cylinder and mix with a fresh charge of air and fuel. Consequently, the power generated by the two-cycle engine is less than it could be if all of the burnt gases where exhausted. In addition, because of the intake and exhaust port arrangement in a conventional engine, the exhaust gases contain large amounts of hydrocarbons and with regard to a two-cycle carburetted engine, raw gas enters directly into the exhaust system.
Further, the performance of a two-cycle engine, especially at low demand conditions such as idle, cruise or coast conditions, is less than desirable and is characterized by excessive stumble and miss firing. This shortcoming can be seen from the following. During idle conditions, that is, when the throttle is virtually closed only a relative small amount of clean air is permitted to enter the combustion chamber. Subsequently, during ignition, the ratio of air to the exhaust gas within the combustion chamber is not sufficient to encourage combustion. During low demand conditions it is not uncommon for a two-cycle engine to misfire four out of five times.
It is an object of the present invention to improve the performance of a two-cycle engine. A further object of the present invention is to selectively control the amount of exhaust gases residing within the combustion chamber of the two-cycle engine such that proper ignition takes place. A further object of the invention is to selectively purge a predetermined amount of working fluid from the cylinder to regulate the effective air/fuel ratio. A further object is to provide a scavenge valve for regulating the performance of a two-cycle engine.
Accordingly the present invention comprises: a method and system for controlling the operation of a two-cycle engine and more particularly for improving engine performance during low demand operating intervals. The method and system are directed to a two-cycle engine of the type comprising a cylinder, including an intake port connected to a source of air, an exhaust port connected to an exhaust system and a scavenge port connect to a passage. The method comprises:
(a) withdrawing the cylinder piston such that the intake port is exposed; PA1 (b) introducing a fresh charge of clean air into the cylinder through the intake port; PA1 (c) maintaining the passage in an open state to permit a predetermined quantity of the fluid within the cylinder to be purged therefrom, through the passage, as the cylinder piston advances toward said scavenge port; PA1 (d) closing the passage after said predetermined amount of fluid has been purged from the cylinder; PA1 (e) compressing the fluid remaining in said cylinder; PA1 (f) introducing fuel into the air; and, PA1 (g) combusting the fluid.
The above method is applicable to both fuel injected and carburetted engines and as such the timing of the introduction of fuel and combustion will be dictated by the engine. The system also provides means for selectively purging fluid from the cylinder of the engine. The cylinder of the type comprising an intake port connected to a source of air, an exhaust port connected to an exhaust system and a scavenge port positioned such that it is preferably covered by the cylinder piston during combustion of the air/fuel mixture within the cylinder. The system further comprises: passage means extending from the scavenge the system additionally includes at least one aperture; a piston slidably situated within the passage means and movable relative to the at least one aperture in response to a force differential, including a first passage formed through a portion thereof. The piston cooperates with the passage means to define a variable volume chamber at a downstream side of the piston. and first means operable in relation to the motion of the cylinder piston for selectively controlling the pressure within the chamber such that in one mode an unbalanced force differential is created to urge the piston in a first direction to permit fluid in the cylinder to be purged therefrom in response to the motion of the cylinder piston, through the at least one aperture and in a second mode a force balanced condition is created to urge the piston in an opposite, second direction, terminating communication through the at least one aperture and hence preventing any further purging of fluid from the cylinder.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.